The invention relates to a method for producing one or more contact connections between a lacquer-insulated wire and one or more contact parts of an electric component by means of soft soldering by employment of divided soldering and a heat source allocated to each solder location. The heat source remains switched on until the contact part or contact parts and the solder are heated to a temperature which suffices in order to guarantee that the lacquer insulation of the wire melts off on the one hand and, on the other hand, that there is a secure contact connection between wire and contact part or, respectively, contact parts.
A method of this type has become known from the German OS No. 2,739,418, incorporated herein by reference. In this known method, the contact piece is applied to one pole, and the wire is applied to the other pole of an electric control current before the solder location or locations are heated. Subsequently, the parts to be contacted and the solder are heated until an electrical contact arises between the wire and the contact part due to the fact that the lacquer insulation of the wire melts off; this electrical contact is employed for shutting off the heat sources. If both wire ends are to be respectively connected to a contact piece, then two heat sources are required. In this case, the one contact piece is connected to the one pole and the other contact piece is connected to the other pole of the control current circuit. The heat sources are then switched off when both contact connections have been produced.
High frequency coils which are connected to a high frequency generator are preferably employed as heat sources for heating the solder locations. Eddy currents arise in the allocated contact part and in the solder due to the high frequency field, so that both parts are successively heated. This is achieved by matching the high frequency generator to the type of parts to be connected. The high frequency energy makes it possible that first the contact piece and the solder are heated due to their relatively large mass. The thin copper wire experiences only a slowly rising heating through the lacquer coating only directly above the solder which becomes molten until the molten tin melts the wire insulation off, whereupon the heat source is then directly shut off. The heat source's influencing time on the solder location is therefore limited to the time which is absolutely necessary. In this manner, it is possible to even solder relatively thin wires to parts with high heat capacity.
If both wire ends of a coil are to be simultaneously soldered--as is always desired in mass production--then a high frequency coil must be provided for each of the two solder locations. In the method described in the German OS No. 2,739,418, the two high frequency loops are then connected in series and lie at a common high frequency generator. A preliminary condition for faultless solder connections, however, is that the two solder locations heat up constantly and simultaneously. This preliminary condition, however, is only present when homogeneous, non-corroding material is employed for the contact parts or when the surface layer thicknesses are constant given electrically treated contact parts. Given different surface layer thicknesses and heating via high frequency, non-uniform heating of the solder locations follows because of skin effect. This results in the fact that individual solder locations can be overheated. Increased spoilage is then the result. In order to prevent the latter, it was hitherto necessary to very precisely monitor the layer thicknesses of the electrical surfaces.